1. The Solar System Discovery Space（1。）.pdfVIP

1. The Solar System The solar system consists of the Sun; the nine planets, over 100 satellites of the planets, a large number of small bodies (the comets and asteroids), and the interplanetary medium (There are also many more planetary satellites that have been discovered but not yet officially named). The inner solar system contains the Sun, Mercury, Venus, Earth and Mars (1, 3) The planets of the outer solar system are Jupiter, Saturn, Uranus, Neptune and Pluto (2, 4) 1 2 3 4 1 The orbits of the planets The orbits of the planets are ellipses with the Sun at one focus, though all except Mercury and Pluto are very near- ly circular. The orbits of the planets are all more or less in the same plane (called the ecliptic and defined by the plane of the Earths orbit). The ecliptic is inclined only 7 degrees from the plane of the Suns equator. Plutos orbit deviates the most from the plane of the ecliptic with an inclination of 17 degrees. The above diagrams show the relative sizes of the orbits of the nine planets. The relative sizes of the planets One way to help visualize the relative sizes in the solar system is to imagine a model in which it is reduced in size by a factor of a billion (109). Then the Earth is about 1.3 cm in diameter (the size of a grape). The Moon orbits about a foot (~30.5 cm) away. The Sun is 1.5 meters in diameter (about the height of a man) and 150 meters (about a city block) from the Earth. Jupiter is 15 cm in diameter (the size of a large grapefruit) and 5 blocks away from the Sun. Saturn (the size of an orange) is 10 blocks away; Uranus and Neptune (lemons) are 20 and 30 blocks away. A human on this scale is the size of an atom; the nearest star would be over 40000 km away.